1. Field of the Invention
The invention relates to a method for the manufacture of unidirectionally fiber reinforced thermoplastics and to apparatuses for carrying out the method.
2. Description of the Prior Art
DE-A 41 21 915 describes a method for impregnating an endless reinforcement fiber strand in a bath which contains a dispersion of thermoplastic particles. In order to obtain an unchanging thermoplastic content in the bath produced, the width of the emerging strand is measured after it leaves the impregnation bath and the measured values thereby obtained are used for the regulation of the particle concentration in the bath. It is proposed to carry out this regulation through the addition of two or more dispersions and thus, for example, to use three dispersions with different concentrations, of which the middle one is set to the expectation value of the concentration in the emerging strand. In this the supply quantities of the dispersions can be set through a level regulation of the bath.
The object of the invention is to further simplify the known method. The simplification is based on it being possible to dispense with a regulation. In this a new recognition is used as the starting point, that a stationary operating state can be set intentionally, namely as a result of the fact that at a constant draw-off speed and at a constant supply of the fed in dispersion, a certain bath concentration sets itself automatically. By means of suitable prior experiments, the correct operating parameters can be determined in order to obtain a desired thermoplastic proportion in the manufacturing bath.
The method for the manufacture of unidirectionally fiber reinforced thermoplastic bands comprises a pressure impregnation of a fiber strand in a bath with a dispersion of thermoplastic particles. Heat treatments for the drying of the strand and a melting on of the particles taken up by the strand follow the pressure impregnation. The strand is drawn through the bath at a predetermined draw-off speed about a plurality of deflection elements. The dispersion of the bath is largely held in a stationary state, namely through the supply of an infeed dispersion with a first particle concentration and through an initial setting of a second particle concentration in the bath: The infeed dispersion is supplied continuously or periodically, with the first particle concentration being held constant. A corresponding feeding in of a dispersion of higher particle concentration as well as an additional amount of dispersing medium is also possible. The second particle concentration is set to a value which remains constant as a result of an automatic self setting alone. In this, the two named concentrations are dependent in an empirically determinable manner on a thermoplastic content of the band to be achieved and on the draw-off speed.
A further new recognition is given by the discovery that there is a definite draw-off speed at which the particle concentration of the infeed dispersion and that of the bath are of equal magnitude. At the draw-off speed with which this equality is associated, the method in accordance with the invention can be carried out in a particularly simple manner.
In the named laying open print DE-A 41 21 915, data on the chemical and physical properties of the usable thermoplastics, reinforcement fibers and dispersing media are provided. These data, which are considered to be applicable, will not be repeated here.